Fix bug in handling Number in Dataset._subset (#183)

An error in a conditional causes the Number class to be used when it
shouldn't, in some cases.

src/anemoi/datasets/data/dataset.py

@@ -168,7 +168,7 @@ def __subset(self, **kwargs):
             bbox = kwargs.pop("area")
             return Cropping(self, bbox)._subset(**kwargs).mutate()
 
-        if "number" in kwargs or "numbers" or "member" in kwargs or "members" in kwargs:
+        if "number" in kwargs or "numbers" in kwargs or "member" in kwargs or "members" in kwargs:
             from .ensemble import Number
 
             members = {}